This invention relates generally to the fabrication of door structure that includes relatively thin plastic paneling; and more particularly is concerned with reinforcing such plastic panel door structure to block or prevent unwanted sagging or other deformation of the door structure that can occur over time as a consequence of temperature changes and imposed weight.
It is found that such deformation or sagging is a serious problem. It can result in misfit of the door in its frame as during door closing, and weakening of the overall door, including interfit of assembled rail and stile plastic components. There is need for a way to prevent such deformation and sagging using lightweight internal means concealed by or covered by plastic paneling.